This invention relates to a tapping machine with a reciprocally movable quill and a spindle, carried by the quill in a forwardly and backwardly rotatable manner, for removably supporting on one end thereof a tap, and more particularly a tapping machine wherein when the quill is suspended of its motion due to the action of an overload release clutch disposed in a power transmitting mechanism between the quill and the drive source, a motor, an overload sensing device senses it immediately for generating a signal, and the quill is returned to the start position based on the signal from the overload sensing device.
In the conventional tapping machines a device for setting a forward stroke of the quill is disposed in a member which is interlocked with a power transmitting mechanism between the motor and the overload release clutch. Therefore, a suspension of the power transmitting by the clutch caused by an overload applied on the quill will not affect the motor rotation, and only when a backward rotation signal from a forward stroke setting device is generated the motor is backwardly rotated to restore the quill to the start position.
As the overload release clutch of this kind a friction clutch is most usually employed. Therefore, even after the suspension of the power transmitting by the overload release clutch, which is a friction clutch, a force to further advance the quill is continuously applied on the friction clutch before the motor begins to be backwardly rotated, which causes various disadvantages such as wear of the friction clutch, damage of parts in the power transmitting mechanism, abnormal overheat of the motor, etc.